The present invention relates to inspection systems and pertains particularly to an improved filter inspection system.
Internal combustion engines, gas turbines, and other air breathing machines are subject to damage from dirt, grit and the like that gets into the intake combustion air that they breathe. Therefore, they must have source of intake air that is clean and free of dirt, grit and debris. Most such machines utilize filters to filter dirt, grit and other debris from the air drawn into the machinery. Most such filters currently in use are of a large cylindrical tubular configuration, with some being tapered somewhat.
The filters are typically formed of inner and outer wire mesh or perforated metal screens, with a corrugated paper filter there between. The filter paper is formed to have a large surface area to allow the passage of air but to trap fine dirt and grit particles. The filter paper is typically formed with a fan or corrugated fold in order to provide a large surface area for the passage of large volumes of air and entrapment of dirt and grit particles. These filters typically cost between thirty-five and eighty-five dollars each. Therefore, filter replacement can become quite expensive when operating in dirty and dusty environments, such as mining, road building and other earth working environments.
It has been customary in the past to clean the filters a limited number of times by washing them in a solvent or the like. The filters can be typically cleaned in this manner two to three times before they must be discarded.
A cleaning system has been recently developed as set forth in U.S. Pat. No. 5,143,529 granted to co-inventor Means herein that further extends the life of filters. That system provides a dry process for cleaning filters that enables them to be cleaned multiple times with no perceptible damage. However, filters do develop small holes from various sources, including cleaning and reuse that render them unusable. These small holes can let sufficient dirt or grit through to severely damage an engine. They usually develop in the crease or fold of the filter paper and are difficult to detect by traditional visual inspection.
Visual inspection of the filters by means of a visible source of light, such as disclosed in Everrod U.S. Pat. No. 4,279,508 is the most common form. However, such visual inspection is subject to the good eyesight, skill and concentration of the inspector. It is also subject to human error and judgment, even with light amplifiers or intensifiers as disclosed in Everrod.
In the aforementioned parent application, there is disclosed improved apparatus using infrared radiation (IR) light sources and IR detectors. However, these also have drawbacks and are not entirely satisfactory.
It is desirable that improved apparatus and methods be available to reliably inspect filters.